Let x be the number of boys in each boy group and let y be the number of girls each girl group have.
We know that the set design crew has two 3 groups of boys and 2 groups of girls and the total number of students is 71, then we have the equation:
Now, for the pit band we have 1 group of boys and 4 groups of girls and the total number os students is 77. hence we have the equation:
Then we have the system of equations:
To determine how many students each king of group have we solve the system; to do this we solve the second equation for x:
Now we plug this value in the first equation and solve for y:
plugging the value of y in the equation for x we have that:
Hence we conclude that each boy group has 13 students and each girl group has 16 students.
Finally the performers crew has one of each kind of group; therefore the performance crew has 29 students.